Method and apparatus for reliably transmitting radio blocks with piggybacked ACK/NACK fields

ABSTRACT

Piggybacked acknowledgement/non-acknowledgement (PAN) bits in unreliable bit positions of a modulated symbol are swapped with data bits located in more reliable bit positions. In addition, a power offset value may be applied to the symbols containing the PAN bits.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.60/957,908, filed Aug. 24, 2007, which is incorporated by reference asif fully set forth herein.

TECHNICAL FIELD

This application is related to wireless communications.

BACKGROUND

The Global System for Mobile Communication (GSM) is one of the mostwidely deployed communication standards for mobile wirelesscommunication. In order to introduce packet-switched technology, generalpacket radio service (GPRS) was developed by the EuropeanTelecommunications Standards Institute (ETSI). One limitation of GPRS isthat it does not support voice services. Other issues with GPRS includelack of higher data rates supported as well as poor link adaptationalgorithms. Therefore, the third generation partnership project (3GPP)developed a new standard for GSM to support high rate data services,released in 1999 and known as enhanced data rates for GSM evolution(EDGE).

A network configured according to these standards comprises a corenetwork (CN), at least one wireless transmit/receive units (WTRU)attached to a radio access network (RAN), such as the GSM/EDGE radioaccess network (GERAN). The GERAN comprises a plurality of basetransceiver stations (BTSs), each connected to and controlled by a basestation controller (BSC). The combination of the BSCs and thecorresponding BTSs is realized as the Base Station System (BSS).

The radio link control/medium access control (RLC/MAC) protocol, whichresides in the WTRU and the BSS, is responsible for reliabletransmission of information between the WTRU and the network. Inaddition, the physical layer latency, (for example, packet transfer andserialization delays) is controlled by the RLC/MAC protocol.

A goal for GERAN evolution is to develop new technology, newarchitecture and new methods for settings and configurations in wirelesscommunication systems. One work item for GERAN evolution is latencyreduction. Release 7 (R7) of the 3GPP GERAN standard introduces severalfeatures that may improve throughput and reduce latency of transmissionsin the uplink (UL) and the downlink (DL). UL improvements are referredto as higher uplink performance for GERAN evolution (HUGE), and DLimprovements are referred to as reduced symbol duration higher ordermodulation and turbo coding (REDHOT). Both of these improvements maygenerally be referred to as evolved general packet radio service 2(EGPRS-2) features.

The Latency Reduction feature includes two (2) technical approaches thatmay operate either in a stand-alone mode, or in conjunction with any ofthe other GERAN R7 improvements. One approach uses a fast positiveacknowledgement/negative acknowledgement (ACK/NACK) reporting (FANR)mode. Another approach uses a reduced transmission time interval (RTTI)mode. A WTRU may operate in both FANR and RTTI modes of operation withlegacy EGPRS modulation and coding schemes (MCSs), and with the newerEGPRS-2 modulation and coding schemes.

REDHOT and HUGE provide increased data rates and throughput compared tolegacy EGPRS DL and UL. These modes may be implemented through the useof higher order modulation schemes, such as sixteen quadrature amplitudemodulation (16-QAM) and thirty two quadrature amplitude modulation(32-QAM). These modes may also involve the use of higher symbol ratetransmissions and turbo-coding. Similar to legacy systems, REDHOT andHUGE involve an extended set of modulation and coding schemes thatdefine new modified information formats in the bursts, various codingrates and coding techniques and the like.

Prior to the introduction of FANR, ACK/NACK information was typicallysent in an explicit message, referred to as an RLC/MAC control block,which contained a starting sequence number and a bitmap representingradio blocks. The reporting strategy (how and when reports are sent, andthe like) was controlled by the network. The WTRU would send a ControlBlock as a response to a poll from the base station system (BSS). Thepoll will also include information about the UL transmission time (forexample, when the WTRU is allowed to send its control block in the UL).During normal operation, when higher layer information is exchangedbetween the WTRU and the network, the information transfer occurs usingRLC Data Blocks.

A drawback of the current ACK/NACK reporting protocols is that a fullcontrol block is needed every time ACK/NACK information is sent.Therefore, a large overhead is required when ACK/NACK information isfrequently needed for delay sensitive services.

Consequently, within the framework of GERAN evolution, a new ACK/NACKstate machine that uses ACK/NACK reports “piggybacked” on RLC DataBlocks in the opposite link direction was introduced.

This protocol has the potential to significantly reduce theretransmission delay without significant overhead. These piggybackedACK/NACK (PAN) reports are bitmaps, designed as a combination of blocksequence numbers (BSNs) which specify outstanding radio blocks bitmapsgiving ACK/NACK information of radio blocks, and size bits or extensionbits specifying the size of the ACK/NACK information. PANs are used totransmit an ACK/NACK bitmap within a radio block carrying RLC data.

This allows for ACK/NACK information to consist either of one single PANor to be split into several multiple segment PANs. This allows for adecrease in latency and round-trip times due to increased flexibility ofsending ACK/NACK reports independently from data transmissions to aparticular wireless transmit/receive unit (WTRU) without necessitatingspecial RLC/MAC control blocks, while maintaining general principles ofRLC window operation.

FIG. 1 shows a conventional radio block. Currently, a PAN field may beinserted into a RLC/MAC radio block using modulation and coding schemes(MCSs) for EGPRS or new MCSs provided by REDHOT/HUGE (EGPRS-2). In bothof these scenarios, the radio block consists of a separately encodedRLC/MAC header 105 that is decodable independent from the RLC datapayload; an RLC data payload 110 and a PAN field 115 that is separatelydecodable from the RLC/MAC header and RLC data payload.

Some legacy EGPRS radio blocks and some new REDHOT/HUGE radio blocks maycontain more than one RLC data Protocol Data Unit (PDU) per radio block.The PAN is mapped on the burst together with the data. The placement ofthe PAN before interleaving is dependent on the interleaving depth ofthe data block. Since all PANs have low code rates, a maximizedinterleaving depth is preferred.

The insertion of the PAN field 115 into the radio block requires heavierpuncturing of the actual RLC data payload. In essence, since the overallnumber of bits that may be placed into the radio block is fixed, moreencoded data bits must be removed from the RLC data payload once a PANis inserted. Since the RLC/MAC header coding remains unchanged even whena PAN is inserted, the coding rate of the data portion should beincreased. However, this may be detrimental to link performance andeffectiveness of the link adaptation algorithm, because the increasedchannel coding rate and reduced number of channel bits of the affectedRLC data payload 110 of the radio block may lead to more transmissionerrors and less protection of the data.

Another problem is that the RLC/MAC header 105, the RLC data payload 110and the PAN field 115 are all independently channel coded. For example,a PAN field, which contains M=20 information bits and N=6 cyclicredundancy check (CRC) bits, is coded into 80 channel coded bitsyielding a coding rate of approximately 0.33. Therefore, balancing errorperformance of the RLC/MAC header 105, the RLC data payload 110 and thePAN field 115 is essential to good performance of the radio block.

The different error performances of the portions making up the RLC MACradio block 110 are shown in FIG. 2. For example, if the error rate ofthe RLC/MAC header 105 becomes too high, more transmissions are lost dueto the receiver (WTRU or base station) failing to decode the RLC/MACheader 105, rather than errors in the RLC data payload 110. Theprotection of the PAN field 115 is also questionable, as well as themapping of the PAN field 115.

In the conventional RLC/MAC radio block of FIG. 1, the RLC/MAC header105, the RLC data payload 110 and the PAN field 115 are interleavedtogether. Their channel-coded bits carried by the modulation symbols arespread across four (4) radio bursts such that bits belonging to the PANfield 115, for example, are not necessarily contiguous. Applying a poweroffset just to a subset of PAN-carrying symbols may create extra leakingof transmit (Tx) power into the adjacent carriers due to radio frequency(RF) non-linearity from “normal” symbols transiting to symbols sent athigher offset power at the configured standard peak-to-average ratio(PAR) back-off for the given modulation order. This may result inintolerable out-of-band emission levels.

It is therefore desirable to have a method and apparatus for linkingperformance and error resilience of different portions of a radio blockand matching portions of a radio block to their respective requirementsfor PAN filed inclusion, when compared to transmission without PAN fieldinclusion, without changing the number of channel coded bits.

SUMMARY

Piggybacked acknowledgement/non-acknowledgement (PAN) bits in unreliablebit positions of a modulated symbol are swapped with data bits locatedin more reliable bit positions. In addition, a power offset value may beapplied to the symbols containing the PAN bits.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example and to be understood in conjunction with theaccompanying drawings wherein:

FIG. 1 is a conventional RLC/MAC block structure for EGPRS datatransfer;

FIG. 2 depicts the error ratios of different portions of a RLC/MAC radioblock without bit swapping.

FIG. 3 shows the structure of a radio block without PAN bit swappingcompared to the structure of a radio block with PAN bit swapping.

FIG. 4 is a block diagram of a wireless communication system including aWTRU and a base station used to transmit and receive radio blocks withpiggybacked ACK/NACK fields.

FIG. 5 is a flow diagram of a procedure performed by the WTRU of FIG. 4.

DETAILED DESCRIPTION

When referred to herein, the terminology “wireless transmit/receive unit(WTRU)” includes but is not limited to a user equipment (UE), a mobilestation, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to herein, the terminology “base station” includes but is notlimited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 3 shows the structure of a burst 300A. The burst 300A includes PANbits 305, header bits 310, and data bits 315. PAN bits 305 areinterspersed throughout the burst and may be found in all bit positionsof a symbol. It is noted that while the burst 300A is representative ofeight phase shift keying (8-PSK) modulation (that is, three bits persymbol), the PAN bit swapping technique disclosed herein may be appliedto any modulation order. Due to the nature of phase shift keyingmodulation, those skilled in the art will recognize that the third bitposition 350 of each symbol is more prone to error than the first twobit positions 340 of each symbol.

FIG. 3 also shows the structure of modulated information bits after PANbit swapping (300B) is applied, according to one embodiment. PAN bits305 in unreliable bit positions 350 of the each symbol (in theillustrated case of 8-PSK, the third bit position of each symbol) are“swapped” with data bits 315 in more reliable bit positions 340. Forexample, PAN bit 305A is shown in burst 300A in the third bit positionof a symbol. After PAN bit swapping, PAN bit 305A has been swapped witha data bit 315 from a more reliable bit position. PAN bit 305B is nowlocated in a more reliable position. After channel coding, the burst isalso accompanied by a training sequence 320, two stealing flags (SF)325, and, in the DL direction, an uplink state flag (USF) 330 fields.

It is noted that PAN bit swapping as disclosed herein improves thereliability of PAN bits 305. However, as a trade off, data bits 315 thatare swapped with PAN bits 305 are less reliable. Due to the importanceof PAN bits 305 and data retransmission techniques, this trade off isgenerally acceptable.

Additionally, areas in the middle of the burst 300A, such as thetraining sequence 320, are less prone to bad channel conditions.Therefore, it may be advantageous to swap PAN bits 305 with other bitsthat are close to the training sequence 320. It would likewise beadvantageous to swap PAN bits 305 with other bits in more desirablelocations of the radio block.

The PAN bit swapping described with reference to FIG. 3 may also beapplied to higher order modulation. More reliable (that is, mostsignificant bits or outer constellation points) of sixteen quadratureamplitude modulation (16-QAM) and thirty two quadrature amplitudemodulation (32-QAM) may be used for PAN bit swapping. Of course, PAN bitswapping as disclosed may be used with any modulation technique havingmultiple bits per symbol.

In addition to PAN bit swapping, one or more power offsets may beapplied to one or more individual portions of the burst 300A to improveperformance. The power offsets may be applied individually or incombination to the header 310, data 315, PAN 305, training sequence 320,stealing flag (SF) 325, and/or uplink state flag (USF) 330 fields, inorder to balance the individual error performance of each of theportions. The power offset or may be adjusted during system operation totake into account varying radio conditions, interference levels, powerheadroom, or presence and absence of individual fields by the radiotransmitter. Accordingly, different power offset values may be appliedto the different fields. By selective application of power offsets tocertain portions of a radio block, link performance may be increasedwhile creating only minimal interference to other receivers.

Referring to FIG. 4, an exemplary method 400 of applying a power offsetas described above begins with initiating a transmission, (step 410). Itis then determined if PAN bits are included in the radio block, (step420). Depending on system operation, PAN bits may always be included sothis step may be unnecessary. If PAN bits are present, the PAN bitslocated in unreliable bit positions are swapped with bits in morereliable bit positions, (step 430), as described above. Next, a poweroffset may be calculated for each various bits and/or regions of theradio block (for example, header field, PAN bits, training sequence,stealing flag), (step 440). Finally, the calculated power offset isapplied to the radio block, (step 450).

In the method 400, the calculated power offset may, for example,counter-balance the effect of an increased coding rate for data bits.The calculated power offset may be applied semi-statically, usingperiodic adjustments, or may be adjusted during system operation to takeinto account varying radio conditions and/or interference levels and/orpower headroom.

A WTRU may independently calculate the power offset values based onpredetermined criteria or measured values, or the WTRU may receive poweroffset values from the network. The network may adjust or configure theoffset values based on link adaptation mechanisms. For example, theoffset value may be signaled to a WTRU in a separate control block, (forexample a packet power control/timing advance, packet time slotreconfigure or packet UL ACK/NACK message). Alternatively, other RLC/MACcontrol blocks may also be modified to convey this type of information.

When PAN bit swapping and power offsets are used in combination, PANbits may be swapped with other bits of a single radio burst among thefour (4) radio bursts that make up a radio block, and a power offset maybe applied to the entire radio burst containing the PAN bits. Thisapproach avoids varying power levels within a burst. Alternatively, thePAN bits may also be swapped with bits of a subset of the four (4) radiobursts that make up the radio block. The power offset may then beapplied to the bursts carrying the PAN bits. These methods may also beapplied to the other bits, such as the header, data bits, and the like.

FIG. 5 shows a WTRU 500 and a base station 505 each configured toimplement the above disclosed methods. The WTRU 500 includes atransmitter 510, a receiver 515, and a processor 520. The transmitter510 and receiver 520 are coupled to an antenna 525 and the processor520. The WTRU 500 communicates with the base station 505 in an uplinkdirection 530 and a downlink direction 535 via an air interface. Theprocessor 520 includes a modulator/demodulator 540, aninterleaver/deinterleaver 545, and a constellation mapper/demapper 550.The processor 520 is configured to produce radio blocks for transmissionand process received radio blocks as described above. Theinterleaver/deinterleaver 545 is configured to interleave anddeinterleave bits in a radio block, and to swap PAN bits with data bitsas disclosed. The constellation mapper/demapper 550 is configured tocode and decode symbols based on a modulation technique, such as QPSK,16-QAM, 32-QAM, or the like, and to swap PAN bits with data bits asdisclosed in cooperation with the interleaver/deinterleaver 545. Themodulator/demodulator 540 is configured to modulate the prepared radioblock for uplink transmission via the transmitter 510 and to demodulatereceived radio blocks in the downlink via the receiver 515.

The processor 520 of the WTRU 510 is further configured to apply poweroffsets to various regions of the radio blocks, as disclosed. Theprocessor 520, in combination with the transmitter 510, may adjust thetransmission power according to calculated or received power offsetvalues, either semi-statically or based on changing channel conditions,as described above. The processor 520 is further configured to receive,via the receiver 515, power offset values from the base station 505.

The base station 505 may contain similar functionality as describedabove with reference to the WTRU 500. A processor of the base stationmay be configured to generate power offset commands as disclosed, and toswap PAN bits as disclosed.

Although the features and elements are described in the embodiments inparticular combinations, each feature or element can be used alonewithout the other features and elements of the embodiments or in variouscombinations with or without other features and elements. The methods orflow charts provided in the present invention may be implemented in acomputer program, software, or firmware tangibly embodied in acomputer-readable storage medium for execution by a general purposecomputer or a processor. Examples of computer-readable storage mediumsinclude a read only memory (ROM), a random access memory (RAM), aregister, cache memory, semiconductor memory devices, magnetic mediasuch as internal hard disks and removable disks, magneto-optical media,and optical media such as CD-ROM disks, and digital versatile disks(DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a WTRU, user equipment (UE),terminal, base station, radio network controller (RNC), or any hostcomputer. The WTRU may be used in conjunction with modules, implementedin hardware and/or software, such as a camera, a video camera module, avideophone, a speakerphone, a vibration device, a speaker, a microphone,a television transceiver, a hands free headset, a keyboard, a Bluetooth®module, a frequency modulated (FM) radio unit, a liquid crystal display(LCD) display unit, an organic light-emitting diode

What is claimed is:
 1. A method for use in a wireless transmit/receiveunit (WTRU), the method comprising: generating a stream of bits fortransmission, the stream of bits including data bits and piggybackedacknowledgement/non-acknowledgement (PAN) bits; interleaving the streamof bits to create an interleaved stream of bits; modulating theinterleaved stream of bits to create a plurality of symbols, whereineach symbol represents a plurality of bits and has a least significantbit (LSB) position, and wherein no PAN bits are present in the LSBposition of each of the plurality of symbols; and transmitting theplurality of symbols.
 2. The method of claim 1, wherein the modulatingthe stream of bits is performed using eight phase shift keying (8PSK)modulation.
 3. The method of claim 1, wherein the modulating the streamof bits is performed using sixteen quadrature amplitude modulation(16-QAM).
 4. The method of claim 1, wherein the modulating the stream ofbits is performed using thirty two quadrature amplitude modulation(32-QAM).
 5. The method of claim 1, wherein the PAN bits are locatedproximate to a training sequence.
 6. The method of claim 1, furthercomprising: applying a power offset value to a transmission powerassociated with each bit of the stream of bits.
 7. The method of claim6, wherein the stream of bits further includes header bits, stealingflags, training sequence bits, and uplink state flag bits.
 8. The methodof claim 7, wherein the applied power offset value is based on a type ofbit of the bit stream.
 9. The method of claim 6, wherein the poweroffset value is calculated by the WTRU.
 10. A wireless transmit/receiveunit (WTRU), the WTRU comprising: a processor configured to generate astream of bits for transmission, the stream of bits including data bitsand piggybacked acknowledgement/non-acknowledgement (PAN) bits; aninterleaver configured to interleave the stream of bits to create aninterleaved stream of bits; a modulator configured to modulate theinterleaved stream of bits to create a plurality of symbols, whereineach symbol represents a plurality of bits and has a least significantbit (LSB) position, and wherein no PAN bits are present in the LSBposition of each of the plurality of symbols; and a transmitterconfigured to transmit the plurality of symbols.
 11. The WTRU of claim10, wherein the modulator is further configured to modulate the streamof bits using eight phase shift keying (8PSK) modulation.
 12. The WTRUof claim 10, wherein the modulator is further configured to modulate thestream of bits using sixteen quadrature amplitude modulation (16-QAM).13. The WTRU of claim 10, wherein the modulator is further configured tomodulate the stream of bits using thirty two quadrature amplitudemodulation (32-QAM).
 14. The WTRU of claim 10, wherein the PAN bits arelocated proximate to a training sequence.
 15. The WTRU of claim 10,further comprising: a transmitter configured to apply a power offsetvalue to a transmission power associated with each bit of the stream ofbits.
 16. The WTRU of claim 15, wherein the stream of bits furtherincludes header bits, stealing flags, training sequence bits, and uplinkstate flag bits.
 17. The WTRU of claim 16, wherein the applied poweroffset value is based on a type of bit of the bit stream.
 18. The WTRUof claim 15, further comprising: a processor configured to calculate thepower offset value.
 19. A method for use in a wireless transmit/receiveunit (WTRU), the method comprising: generating data bits and piggybackedacknowledgement/non-acknowledgement (PAN) bits; generating a pluralityof symbols based on the data bits and the PAN bits, wherein each symbolof the plurality of symbols represents a plurality of bits and has aleast significant bit (LSB) position, and wherein no PAN bits arepresent in the LSB position of each of the plurality of symbols; andtransmitting the plurality of symbols.
 20. The method of claim 19,wherein the generating the plurality of symbols includes: channel codingthe data bits and PAN bits to generate channel-coded bits; interleavingthe channel-coded bits to generate interleaved bits; and modulating theinterleaved bits to generate the plurality of symbols.
 21. The method ofclaim 20, wherein the modulating the interleaved bits includes usingeight phase shift keying (8PSK) modulation, sixteen quadrature amplitudemodulation (16-QAM), or thirty two quadrature amplitude modulation(32-QAM).